The structure of Atom IV
Symbol of elements
1. A symbol of element is the chemical 4. If there are two or more elements that
symbol written in short form to represent have mane start with the same alphabet
a particular element. letter, a second letter is added to
2. Each element is represented by a symbol, differentiate between these elements.
consisting of either one letter or two 5. The second letter used is always
letters of the alphabet. lowercased.
3. Some elements are represented by the first Examples
letter of its name. Elements Symbol
Examples: Bromine Br
Element Symbol Calcium Ca
Fluorine F Chlorine Cl
Hydrogen H Chromium Cr
Iodine I Magnesium Mg
Nitrogen N Manganese Mn
Oxygen O Neon Ne
Phosphorus P Nickel Ni
Sulphur S Silicon Si
6. Some elements are represented by their Latin names. For example,
Elements Latin Name Symbol
Copper Cuprum Cu
Iron Ferrum Fe
Lead Plumbum Pb
Mercury Hydrargyrum Hg
Potassium Kalium K
Silver Argentum Ag
Sodium Natrium Na
Tin Stannum Sn
Isotopes and their Importance
Isotope 2. It can also can be defined as atoms of
1. Isotopes are atoms of certain elements certain elements with the same proton
which have the same number of protons numbers but with different nucleon
but different number of neutrons in the numbers.
nucleus of the atoms.
Three important points to define isotopes.
• Isotopes are different atoms of the same element.
• Isotopes have the same number of protons or same proton numbers.
• Isotopes have different numbers of neutrons or nucleon numbers.
Properties of Isotope
Number of proton equal
Number of neutron difference
Chemical properties same
Physical properties difference
Element Name Symbol Proton Nucleon Number of Number of
Number Number proton neutron
Hydrogen Hydrogen 1
H 1 1 1 0
H 1 12 1 1
H 1 23 1 2
Oxygen Oxygen-16 16
O 8 16 8 8
O 8 17 8 9
O 8 18 8 10
Carbon Carbon-12 12
C 6 12 6 6
C 6 13 6 7
C 6 14 6 8
Chlorine Chlorine-35 35
Cl 17 35 17 18
Cl 17 37 17 20
Sodium Sodium-23 23
Na 11 23 11 12
Na 11 24 11 13
Uses of isotopes in our daily lives
1. There are two types of isotopes, namely 3. Radioisotopes have many applications in
a. the stable isotopes (non-radioactive) daily life.
b. the non-stable isotopes (radioactive). 4. Several uses of radioisotopes in daily life
2. Unstable isotopes go through radioactive are shown in Table below.
decay and emit radiation and they are
known as radioisotopes.
Medical Gamma rays of cobalt-60 are used to kill cancer cells without surgery in
patients. This treatment is known as radiotherapy.
Patients with skin cancer can be treated using beta rays from the isotopes
phosphorus-32 and strontium-90
Medical instruments such as surgical equipment, syringes and bandages
can sterilize by using gamma rays.
Radioisotopes are also used as tracers.
A small amount of sodium-24 is injected into the patient's body.
A radioactive detector is then used to detect accumulation of sodium-24
and therefore detect tumours and blood clots before they become
This tracing method is also used to investigate the thyroid glands by
measuring the uptake of iodine-131.
Plutonium-238 in a nuclear battery is used to produce small electric
shocks in the heart pacemaker.
People with irregular heartbeats need to have a heart pacemaker
implanted inside their chest.
The nuclear battery of the pacemaker provides a tiny electrical shock to
ensure a steady heartbeat.
Agricultural Radio isotopes are used to cause mutation in insects so as to make them
sterile or to cause death. These serve as pest control in agriculture.
The metabolism of phosphorus by plants can be studied using phosphate
fertilisers that contain phosphorus-32.
A small amount of phosphorus-32 is used in fertilisers.
The radiation produced by phosphorus-32decaying is detected by a
This method can trace the passage of phosphate ions in plants..
Carbon-14 is used to study the passage of carbon during photosynthesis in
Industrial Isotope sodium-24 is used to detect leakage of underground pipes.
Beta rays are used to control the thickness of plastic, paper and metal
sheets in factory.
Gamma rays are used to detect whether cans or bottles are filled up to the
Sodium-24 is used to measure the wear out rate of engine in a vehicle.
Food Preservation The gamma rays from cobalt-60 are used to kill bacteria in food to make
fresh vegetables and fruits last longer without any change in quality,
flavour and texture of food.
Gamma rays are used to inhibit budding in potatoes.
Archeology Radioisotope carbon-14 is used to study and estimate the age of ancient
artifacts. This method is named as the radiocarbon dating.
Production of Energy Plutonium is used in nuclear reactors to produce electrical energy.
5. Radioactive isotopes are very dangerous 7. Long-term exposure to radioactive rays
if it is misused. may
6. Short-term exposure to radioactive rays 1. cause mutation in our
may genes and abnormalities in newborn
a) kill or destroy the cells in our body babies
and cause organ damage 2. disturb the growth and
b) cause rashes and burns on the exposed division of cells and consequently
skin cause cancer
Electron Configuration in Atom
1. We have learnt that electrons occupy 7. However, with the third shell, when eight
orbits with definite energy level of an electrons are present, extra stability is
atom, as suggested by Neils Bohr. gained. The additional electrons go into
2. These orbits with definite energy level the fourth shell before the third shell is
are known as the shell. completely filled.
3. Every single shell is capable of holding 8. The way in which the electrons are
up to certain amount of electrons. distributed in the shells of an atom is
4. The first shell can hold up to two called the electron arrangement or
electrons. This is called a duplet. electron configuration of the atom.
5. The second shell can hold up to eight 9. The examples below show the electron
electrons. This is called an octet. arrangement of some elements:
6. The third shell can hold up to eighteen
Atom Notes Electrons Arrangement
1. Lithium has 3 protons and 3 neutrons and three
electrons as well.
6 2. All the three electrons are arrange as follows:
3 Li • Two electrons are filled in the first shell.
• One electron is filled in the second shell.
• The electron arrangement of carbon is 2.1
1. Chlorine has 17 protons and 18 neutrons and 17
2. All the three electrons are arrange as follows:
35 • Two electrons are filled in the first shell.
17 Cl • Eight electrons are filled in the second shell.
• Seven electrons are filled in the third shell.
• The electron arrangement of chlorine is
1. Calcium has 20 protons and 20 neutrons and 20
2. All the three electrons are arrange as follows:
• Two electrons are filled in the first shell.
20 Ca • Eight electrons are filled in the second shell.
• Eight electrons are filled in the third shell.
• Two electrons are filled in the forth shell.
• The electron arrangement of carbon is
Element Proton Number Number of electron in Electron
Number of Arrangement
1st shell 2nd shell 3rd shell 4th shell
Hydrogen 1 1 1 0 0 0 1
Helium 2 2 2 0 0 0 2
Lithium 3 3 2 1 0 0 2.1
Beryllium 4 4 2 2 0 0 2.2
Boron 5 5 2 3 0 0 2.3
Carbon 6 6 2 4 0 0 2.4
Nitrogen 7 7 2 5 0 0 2.5
Oxygen 8 8 2 6 0 0 2.6
Fluorine 9 9 2 7 0 0 2.7
Neon 10 10 2 8 0 0 2.8
Sodium 11 11 2 8 1 0 2.8.1
Magnesium 12 12 2 8 2 0 2.8.2
Aluminium 13 13 2 8 3 0 2.8.3
Silicon 14 14 2 8 4 0 2.8.4
Phosphorus 15 15 2 8 5 0 2.8.5
Sulphur 16 16 2 8 6 0 2.8.6
Chlorine 17 17 2 8 7 0 2.8.7
Argon 18 18 2 8 8 0 2.8.8
Potassium 19 19 2 8 8 1 126.96.36.199
Calcium 20 20 2 8 8 2 188.8.131.52
1. The electrons in the outermost shell of an atom are called valence electrons.
2. The valence electrons have great significance in determining the chemical properties of
3. Elements with the same number of valence electron have the same chemical properties.
Particle Proton Nucleon Electronic Number of Valence
Number Number Configuration Electrons
P 6 12
Q 6 14
R 8 16
S 11 23
T 17 35
1. Table above shows the proton number and nucleon number of particle P, Q, R, S and T.
a. Define proton number and nucleon number.
b. What is the number of electrons in one particle R?
c. Find the number of nucleons in one particle Q.
d. Write the electronic configuration and number of valence electron for all theparticles in the
e. Draw the atomic structure of particle P and T.
f. How many shells are fill with electron in an atom of particle S.
g. What is mean by isotope.
h. Which of the two particles are isotopes?
i. Write down two similarities and two differences of isotopes.
2. The structure of a sodium particle is shown in the figure above. Answer the following question
base on the figure above.
a. What is the proton number and nucleon number of sodium?
b. What is the charge of the particle? Give a reason to your answer.
c. What is the electronic configuration of the sodium particle?
d. The sodium particle has how many valence electrons?